DESCRIPTION As the result of strokes, tumors, or brain trauma, many people suffer from sensory neglect. Often this includes an inability to direct attention to a portion of the visual field or to sensations from an area of the body, even through the fundamental neurocircuitry remains intact. The goal of this research is to understand the functional anatomy of somatosensory perception, in particular the neural mechanisms involved in directing attention to touch and localizing it in space. Current knowledge of the influence of attention on somatosensory processing remains unresolved. In addition, no studies with normal human subjects have explored the neural basis for localizing touch in extra-personal space. Studies of tactile subjects have explored the neural basis for localizing touch in extrapersonal touch location in a body centered reference frame. Pilot data collected in our lab supports such a representation such a representations in normal subjects. We propose using 150-labeled water and positron emission tomography (PET) to address the following two specific aims: 1) to determine the effect of attention on somatosensory cortex in the preference and absence of a stimulus and 2) to identify the neuroanatomical substrate for the spatial representation of touch.